This disclosure generally relates to medical monitoring systems and devices, and more specifically to leadwires for ECG and/or respiratory monitoring.
Electrocardiograms (ECGs) are graphic depictions of electrical activity in the heart, i.e. cardiac potentials. ECGs are produced by electrocardiographs which are available as stand alone devices, portable devices, and/or as integrated functions in various types of multi-vital sign monitoring devices. ECGs are depicted by time (ms) versus voltage (mV) and typically are represented as a waveform. The typical five important aspects, or portions, of an ECG waveform are the P wave, QRS complex (represented as the combination of the Q, R, and S waves respectively), and T wave. The less frequently seen sixth portion is a U wave. The data produced from the graphical depictions are useful in diagnosis of patients to determine what, if any, and the extent to which heart-related problems exist in a patient.
Respiration monitors are also available that use chest electrodes that are similar or identical to ECG electrodes. For example, respiration rate measurement may be determined using impedance pneumography, where a high-frequency A/C current is passed between at least two electrodes (often the right arm electrode and left arm electrode), including a driving electrode and a receiving electrode, on the patient's chest and an impedance between the electrodes is determined. Respiration is then monitored according to the changing impedance values as the patient breathes. As the patient inhales, air (which is an insulator) enters the lungs and causes the net impedance in the circuit to increase. When the patient exhales, air leaves the lungs and causes the impedance in the circuit to decrease.
Both electrocardiographs and respiration monitors (which may be separate devices or contained in a single device using a common set of electrodes) must have protection circuitry to protect the electronics of those devices from high voltage exposure due to operation of a defibrillator on a patient to which the monitoring devices are connected. Patients experiencing sudden cardiac arrest are treated with a defibrillation shock to the chest. The defibrillation shock is typically in the range of 3 to 5 kilovolts and 50 amps, and typically lasts between 5 and 20 milliseconds. Such a high voltage and current are necessary in order to stop the patient's heart from unproductive fluttering (fibrillating) and to allow the heart to restart effective pumping of blood. Typically, respiration monitors and electrocardiographs are separate from the defibrillator device, and the chest electrodes and leadwires are connected to the patient when the defibrillator delivers the shock. Thus, the electrocardiograph and respiration monitors must withstand the significant voltage and current of the defibrillation and continue working properly.